To achieve highly efficient warehouse operations, it is desirable to accurately track the movements of pallet loads and other objects to be located and/or transferred within the warehouse as they are transported to and from various locations, such as storage locations, stocking locations, staging areas and loading docks. In typical conventional warehouse management operations, the operator of a transport vehicle, such as a fork truck, reach truck, lift truck or pallet truck, receives a set of printed stocking or picking orders, typically generated by a computer, and executes the orders by visually identifying the loads and locations and transporting the loads to and from the locations specified on the orders. In such a system, especially in large-scale warehouses with a large number of locations and loads to handle, there are numerous opportunities for errors.
Radio-frequency identification (“RFID”) tag systems have been proposed for use in inventory tracking. In such a system, an RFID tag is attached to an object or location, and contains a non-volatile memory for storing information identifying the object or location and electronic circuitry for interacting with an interrogator. RFID tags may be passive or active. In the case of a passive RFID tag, the tag includes circuitry for converting at least a portion of the received RF signals into electrical power needed by the tag for signal processing and transmission. In a typical conventional system, RFID tags containing information associated with the identities of inventory items to be tracked are attached to the inventory items. An RFID interrogator is used to detect the presence of an RFID tag and read the identification information from the tag. A typical RFID interrogator includes an RF transceiver for transmitting interrogation signals to and receiving response signals from RFID tags, one or more antennae connected to the transceiver, and associated decoders and encoders for reading and writing the encoded information in the received and transmitted RF signals, respectively. The interrogator may be a portable device, which can be brought near the tags to be read, or it may be a stationary device, which reads the tags as they are brought to the interrogator, as in the case of tagged library books being returned to a return station that is fitted with an interrogator. RFID tags may also be affixed near a location as a location marker. After detecting both a tag attached to an inventory item and a location marking tag, a processing unit associated with the interrogator may determine that the inventory item is positioned near the tagged location. While these conventional object tracking systems are capable of keeping a record of the inventory items and sometimes their locations, they are not effective for tracking and/or managing the movement of the inventory items.
There also exist warehouse inventory tracking systems that include fixed RFID interrogators at various locations to detect RFID-tagged items when they are positioned near the interrogator-equipped locations. For example, there are warehouses with RFID interrogators positioned at or near the loading dock gates. Such systems are capable of tracking the arrival of tagged items at the various locations, but are not capable of detecting errors remote to these locations. For example, if a fork truck picked up a wrong load because the truck was driven to a wrong pick-up location, the error would not be detected until the load had reached the gate. This delayed error detection negatively impacts the overall efficiency of warehouse operations. Additionally, outfitting each of the numerous loading dock gates with an interrogator is not cost effective.
Radio Frequency Identification (RFID) is a technology that uses hardware devices, called transponders or tags, to store data. The data on such a tag can be read and written by RFID Readers in a contact-less manner using radio waves. The RFID technology has attracted a very high-level of interest in the industry. This is especially true in the Consumer Packaged Goods (CPG) and Retail Industries where the benefit of using RFID is readily apparent. But as with any new technology, the standards are not defined and even when these are defined components several aspects of the solution are either unspecified or is a part of the future roadmap. However, the RFID technology is still being matured to provide solutions to business problems. A very common open problem is tagging real-world objects with RFIS tag so that RFIS readers can successfully read them. Because of virtually infinite combinations of material, packaging, orientation and other factors tagging a simple real-world object can be difficult if not impossible.
A very common need of the business community is to tag items that are in a pallet. Now these items could be individual items like cans of paint or acid or boxes of cans. Radio waves perform extremely poorly if placed on metal and liquid items. Also, even if tags are placed on containers made of metal or containing liquid then all of these containers cannot be read by RFIS readers as there is a limitation as to how much the radio waves can penetrate inside a pallet that contains several containers. Also, another problem in the business community is shrinkage, which refers to stolen or lost items during production. Thus, for example, a case containing 5 large cans of soup is tagged using an RFID tag, and someone takes one of the soup cans out of the case. There is no way of knowing that by just reading the tag data. Thus, the problem is two-fold:
(1) How to read a large number of items on a pallet successfully if the items are made of non-friendly material?
(2) How to dynamically determine if some of the items have been stolen from the pallet?
There remains a need for a radio frequency identification tag that can be used on non-friendly materials and can detect when there is a change in the number of items in a sealed package.